1. Field of the Invention
The present invention relates generally to a catalyst for converting carbon monoxide and oxygen into carbon dioxide. More particularly, the present invention relates to a catalyst comprising platinum black deposited on platinum wire which is effective for converting carbon monoxide and oxygen to carbon dioxide at a moderate temperature within the range of about 150 to 300.degree. C.
2. Description of Related Art
In a carbon dioxide (CO.sub.2) laser system, carbon dioxide, which is the active lasing medium, is contained in a sealed laser cavity which also houses a pair of electrodes for applying an electric discharge to the carbon dioxide. When a electric discharge is applied, laser emission is produced by the CO.sub.2. However, the electric discharge also dissociates the CO.sub.2 into carbon monoxide (CO) and atomic oxygen (0), as indicated by Equation (1) below. EQU CO.sub.2 .fwdarw.CO+O (1)
The atomic oxygen so formed then reacts with itself to form molecular oxygen (O.sub.2) as shown in Equation (2). EQU O+O.fwdarw.O.sub.2 (2)
The net reaction is the conversion of carbon dioxide to carbon monoxide and molecular oxygen as shown in Equation (3). EQU CO.sub.2 .fwdarw.CO+1/2O.sub.2 (3)
The oxygen formed by this process causes a rapid loss in laser power and other erratic discharge behavior including arcing. Thus, it is desirable to remove this oxygen. To accomplish this result, it has been the practice in the art to use a catalyst to promote the reaction of the CO and O.sub.2 to re-form the CO.sub.2 starting material. One such catalyst comprises an electrically heated platinum wire which operates at 1000.degree. C., as disclosed, for example, by D. S. Stark and M. R. Harris, in the publication "Platinum-Catalysed Recombination of CO and O.sub.2 in Sealed CO.sub.2 TEA Laser Gases," J. Phys. E: Sci Instrum, Vol. 11, 1978, pages 316-319. However, the use of this high temperature is undesirable because it requires increased power input and generates heat, which may lead to distortion of the laser cavity or optical bench. Another catalyst which has been used for this purpose is Hopcalite, as disclosed, for example, by R. B. Gibson et al, in the publication "Sealed Multiatmosphere CO.sub.2 TEA Laser: Seed-gas Compatible System Using Unheated Oxide Catalyst," Appl. Phys. Lett., Vol. 32, No. 11, 1978, pages 726-727. Hopcalite is a mixture of 60 percent magnesium oxide and 40 percent cuprous oxide that is provided in powder or granular form, and is available from Mine Safety Appliances Company of Evans City, Pa. Unfortunately, very small particulates from the granules become dispersed throughout the laser cavity and cover the optical elements, thus degrading the laser performance. In addition, Hopcalite has been found to rapidly deactivate when stored in a laser gas mixture or in the presence of water. Other catalysts which have been used for this purpose comprise mixtures of noble metal catalysts on ceramic substrates, as disclosed for example in U.S. Pat. No. 4,639,432. However, such catalysts are sensitive to contamination or lack the required activity.
Consequently, there exists in the field of carbon dioxide lasers the need for a catalyst for removing oxygen and, in particular, for reacting the oxygen and carbon monoxide by-products to form carbon dioxide, which is effective at moderate temperatures and is not easily contaminated. This catalyst would also be desirable for other applications where carbon monoxide and oxygen are combined to form carbon dioxide or where oxygen must be removed in the presence of carbon monoxide.